A burner arrangement is known, for example, from EP-A1 0 597 138.
Nowadays, annular low-NOx (EV) combustion chambers (EV=Environmental) for gas turbines with a single row of burners are considered proven technology (cf. for example F. Joos et al. “Development of the sequential combustion system for the GT24/GT26 gas turbine family”, ABB review 4, 1998 pp. 4–16 (1998)). The burners in these gas turbines/combustion chambers can be removed through corresponding access openings in the outer turbine casing.
Other gas turbines (e.g. of type GT13E in the name of the Applicant) have a two-row arrangement of burners in the annular combustion chamber, as shown for example in FIGS. 1 and 3 of document EP-A1 0 597 138. In the form shown there (with pairs of burners oriented parallel), a two-row arrangement of this type can only be realized on account of the fact that the burners cannot be removed outward, but rather have to be removed by being pulled inward into the combustion chamber. The combustion chamber has to be large enough for this to occur and must also be externally accessible through a special manhole (cf. FIG. 2 of EP-A1 0 597 138 and the associated description). The openings for the fuel feedlines in the turbine casing may in this case be small.
One drawback of the known two-row burner arrangement is the complex access to the combustion chamber via corresponding manholes which is required to change the burners. A further drawback is the operation of changing the burners, which is time-consuming in this solution. The provision of access openings in the turbine casing, through which the burners can easily be pulled out in the outward direction, however, causes problems with regard to the mechanical integrity of the turbine casing. The turbine casing has to satisfy certain mechanical demands and should not be deformed or crack under pressure and thermal loading. Therefore, it is necessary to maintain a minimum distance between access openings of this type in the outer turbine casing. This is highly important in particular in the case of double-row burner arrangements.
Furthermore, in any combustion chamber it is desirable for the hot gases to be thoroughly mixed in the primary zone. Therefore, particularly in the case of burner arrangements with two or more rows, it is necessary to find ways of achieving a mixing which is sufficient even under part-load operation, in which the operation of the burners is stepped down.
Finally, it is observed that the burners produce hotspots on the inner linings of the combustion chamber, where the hot gas flowing out of the burners impinges on the walls.
U.S. Pat. No. 5,829,967 has disclosed a combustion chamber with two-stage combustion. It has a primary burner of the premixing type, in which the fuel injected via nozzles, inside a premixing space, is intensively mixed with the combustion air prior to ignition. The primary burners are designed to have a flame-stabilizing action, i.e. without mechanical flame holders. They are provided with tangential flow of the combustion air into the premixing space. Downstream of a preliminary combustion chamber there are secondary burners, which are designated as premix burners that are not independent. U.S. Pat. No. 3,724,207 also discloses a combustion chamber.